Prop settings

[Jamie]

I must be searching for the wrong stuff because a search turned up zilch on this.

I've been taught to use 2700rpm (prop full forward) and 23" mp in cruise. Looking at the POH tables, that appears to give me max speed up through 10,000ft, where 23" isn't possible any longer without a turbocharger.

In my airplane the only time the prop control is pulled back is during runup. After that it stays fully forward. From what I've been able to find out about constant speed prop operation, this isn't hurting anything (it's where you want it for take off, it gives you max speed in cruise, and it adds drag for descent, it's even where it should be for a go around).

So when would I want to select a lower rpm? What do you guys do?

[dcastor]

I'm not going to contradict the POH, but I find that a couple hundred RPM reduction reduces the nose significantly in the cockpit and doesn't have a big impact on speed.  Also, I think I've noticed based on my fuel flow monitor a reduction in fuel consumption with slower RPM - which makes sense.

[aaronk25]

2700rpm is perfect, except if you don't have to get there as fast you can boost your mpg by 10-20% by slowing it down, consequently you also slow down some, but if your not running on a fuel budget what the heck let er eat...

[aaronk25]

One other thought because engine time is directly related to the speed of the engine you will be running through time faster than cruising at 2500rpm

[kmyfm20s]

One other thought because engine time is directly related to the speed of the engine you will be running through time faster than cruising at 2500rpm

What RPM equals an hour of engine time?

[RJBrown]

Oil consumption can be more at 2700 than 2500. Prior to my recent O\H oil usage was much greater at 2700.

[bumper]

Higher RPM means more explosions per minute and thus more power available - ignoring everything else. Some of that "else" is prop effeciency, and this may be important to you in cruise. Turning the prop slower, especially with some prop designs, really boosts effeciency, lowering fuel consumption while having a minimal effect on speed. Over square and LOP is a good place to be.

[Super Dave]

If you're up for some reading, check out John Deakins "Pelicans Pearch" engine management articles on AvWeb. Lots of well writen information on prop, manifold pressure, and mixture settings.

[PilotDerek]

If you're up for some reading, check out John Deakins "Pelicans Pearch" engine management articles on AvWeb. Lots of well writen information on prop, manifold pressure, and mixture settings.

Those articles were required reading by my instructor when I was getting my complex training.

[OR75]

I must be searching for the wrong stuff because a search turned up zilch on this.

I've been taught to use 2700rpm (prop full forward) and 23" mp in cruise. Looking at the POH tables, that appears to give me max speed up through 10,000ft, where 23" isn't possible any longer without a turbocharger.

In my airplane the only time the prop control is pulled back is during runup. After that it stays fully forward. From what I've been able to find out about constant speed prop operation, this isn't hurting anything (it's where you want it for take off, it gives you max speed in cruise, and it adds drag for descent, it's even where it should be for a go around).

So when would I want to select a lower rpm? What do you guys do?

 

 

prop RPM and MP ... very similar to gear and gas pedal on a manual transmission car

 

on highway (ie flight level): high gear (lower RPM) / easy on the gas pedal 

 

start (climb): low gear (high RPM) / press on the gas pedal 

 

of course, if you want to get some real torque, shift to lower gear (high RPM)  and press on the gas (high MP). It does gets noisier and you use more gas but you do get the torque you want to pass everyone. 

[Alan Fox]

What RPM equals an hour of engine time?

2545 rpm = tach hours .....  Running at 2300 = more flying time between overhauls......... Less rpm = less wear on engine components and accesories....

[FloridaMan]

Previous owner of my plane said he chose the RPM that minimized vibrations and he'd look at the bubbles at the top of the compass to find it. I've had the vacuum pump and the manifold pressure line break since I got the airplane and I would have to think that both of those could have been aggravated by vibration. 

[jetdriven]

Shouldnt be bubbles inthe compass.  IIRC the correct recording speed for a Mooney is  2566 RPM.

[bumper]

Previous owner of my plane said he chose the RPM that minimized vibrations and he'd look at the bubbles at the top of the compass to find it. I've had the vacuum pump and the manifold pressure line break since I got the airplane and I would have to think that both of those could have been aggravated by vibration. 

 

Dynamic prop balance?? I have an Aces 2020 balancer, so I know mine is spot on.  I can't imagine putting up with a prop that puts bubbles in the compass (but then I have a vertical card with no fluid).

 

When a prop is out of balance, all the energy that is used to shake things up and fatigue the airframe is wasted energy that could better be used to make things move through the air faster or consume less fuel. Vibration is not free!